The present invention grew out of the inventor's experience with mass production wood lathes used for turning wood blocks into bedposts, table legs, chair parts, stair parts and similar items.
A long-popular lathe for use in such production is the Mattison No. 57-F, 54" Automatic Shaping Lathe, made by the Mattison Machine Works, of Rockford, IL.
On such a lathe, a cutterhead, or a series of cutterheads, is mounted on an arbor on the lathe and turned at high speed, typically 2700 RPM. The wood block to be turned is clamped between the head stock and tail stock of the lathe and carried into the cutterhead.
Balancing problems which have long faced craftsmen working in the field of setting-up and operating such lathes typically cause 4-6 hour set-up times and lead to overlap problems (when eccentricity results in some knives cutting more than others).
The tooling mounted to an arbor for turning a wood block typically includes at least one cutterhead. Where the length of the part to be turned requires, two or more cutterheads are mounted axially adjacent one another in series on the arbor. Each cutterhead is assembled from a T-slot cylinder (the part which mounts directly on the arbor), knife holders (which mount in the T-slots on the faces of the cylinder), and the knives (which mount to the holders, and do the actual cutting).
A T-slot cylinder typically has six or eight faces (e.g., it is hexagonal or octagonal in transverse cross-sectional shape), is two to fourteen inches long and each face is centrally provided with a longitudinally extending radially outwardly opening T-shaped slot in which, in use, one or more knife-holders is removably mounted. An assembled cutterhead may weigh up to 200 pounds.
Typical T-slot cylinders of the type with which the present invention is concerned, are shown in the U.S. Pat. No. of M.W. Mattison, 1,222,783, issued Apr. 17, 1917, and the U.S. Pat. No. of C.L. Mattison, 1,710,097, issued Apr. 23, 1929. Apparently because the two Mattison patents are mostly concerned with how to mount the cutters on the cylinder, rather than how to mount the cylinders on the arbor, they do not disclose the latter. However, the means conventionally used for mounting T-slot cylinders on arbors is shown in the U.S. Pat. No. of Ensign 1,072,930, issued Sep. 9, 1913.
In the conventional set-up, the T-slot cylinder has two one-half inch set screw holes tapped into the same one face of the cylinder between a corner where the respective face intersects an adjacent face, and the T-slot in the respective face. The set screw holes are typically located three-quarters of an inch in from the respective ends of the cylinder.
If a lathe arbor is substantially true and a conventional T-slot cylinder 3, with its set screws loosened, is slid onto the arbor, and the arbor is slowly rotated while a conventional eccentricity-measuring gauge is operated against the arbor, the gauge typically will show that the arbor is rotating within two thousandths of an inch of true. However, as the two set screws are tightened as is necessary for locking the cylinder in place on the arbor, and the arbor is slowly turned again, with the conventional measuring device operating, it is typical for an out of balance condition of two to fifteen thousandths of an inch (most typically 5-6 thousandths of an inch) to be indicated. In general, the longer the cylinder, the worse the problem.